The coefficients appearing in Eq. REF  are generally fitted to reproduce either the experimental or ab initio data available for a specific compound and provide a compact representation of a magnetic system's spectral properties[1]}, [2]}, [3]}. The values of the spin Hamiltonian's coefficients are strongly dependent on the spin environment and they can be used as an analytical instrument to investigate the relation between chemical structure and magnetic/electronic properties. The strong dependence of the coefficients of Eq. REF  with respect to molecular structure is not limited to radical changes such as the replacement of ligands or the change of an ion's coordination number. In fact, the sensitivity of magnetic properties with respect of structural distortions is so strong that even small molecular distortions due to thermal strain are able to modulate the coefficients of the spin Hamiltonian[4]}. Therefore, molecular dynamics introduces a time dependence into the spin Hamiltonian \(\hat{H}_{s}(t)\) . Such time dependency acts as a perturbation of the equilibrium degrees of freedom and it is at the origin of spin-lattice relaxation itself.
